Heat exchangers with electrical resistance heater elements are commonly used for heating fluids in processing plants, such as chemical plants. Typically, a number of electrical resistance heater elements are located within a tank of the heat exchanger. Each heater element 21 comprises a metal tube containing a coiled resistance wire for generating heat as electrical current passes through it. The coiled wire is insulated from the metal tube by an insulation powder, which is typically magnesium oxide packed tightly within the tube surrounding the coiled wire. While magnesium oxide provides excellent electrical insulation, it is a desiccant, thus it attracts moisture from the surrounding atmosphere. The penetration of moisture reduces the ability of the insulation powder to insulate.
In the past, heater elements of this nature have been kept in low humidity rooms and/or baked in an oven with their ends open to drive off any moisture. Then, when ready for use, the heater element is mounted to a header plate and seals are placed over the open ends. For example, a liquid sealant may be poured over the open ends and cured. While these methods work, improving the resistance of the insulation is desirable.